Hi Andrew,
Re the second tail you suspected on C/2017T2 does the attached image from Daniel Pivato help clarify matters. I think that there have been images posted showing a second tail at times over the past couple of months. A trawl through the images in the BAA Comet Archive may turn them up.
Best wishes
Denis

https://britastro.org/cometobs/2017t2/thumbnails.html

On Sunday, 17 May 2020, 09:38:49 BST, Andrew Robertson <andrew@fast-mail.net> wrote:

Morning Nick,

I had a visual on Y4 last night in the 12" Mewlon, it was below 14 degrees altitude and is very faint now, couldn't see it in the 4" Vixen Fluorite. Used 50mm Tak LE and 40 mm Pentax giving x71 & x89 respectively but same FOV at 44'. Very diffuse and elongated over a 1/4 FOV i.e. greater than 11' long. I could see a slightly brighter elongated patch towards the head, but off centre to the left in my inverted straight through view.

Y1 is also getting very faint now but T2 is very bright and prominent, a bright coma with a longish narrow tail. I keep thinking I can detect a 2nd shorter more tenuous tail at 60 degrees to the main but not seeing this in any of the images so perhaps averted imagination on my part.

I did get a glorious view of T2 on the 15th just after M/N, it was in the same FOV as two 12th magnitude GX's - ngc's 2633 & 2634, in fact I was picking up a 3rd AV, that was ngc 2634A at mag 14.2. Haven't seen any images of that view so far so I do wonder if T2 is being neglected a bit at the moment in favour of Y4.

Andrew

-----Original Message-----
From: baa-comet@simplelists.com [mailto:baa-comet@simplelists.com] On Behalf Of Nick James
Sent: 17 May 2020 08:33
To: baa-comet@simplelists.com
Subject: [BAA Comets] C/2019 Y4 on May 16

I think we can safely say that C/2019 Y4 will soon be redesignated
D/2019 Y4. It faded another 0.5 magnitudes from May 15.9 to 16.9 and there is no photocentre left for astrometry. All that we see now is two fading trails of debris.

It is a very challenging target now as it dives towards the northern horizon but please keep imaging it if you can.

Nick.
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